1. Field of the Invention
The present invention relates to a multi-layer structure and method of drawing a microscopic structure therein, an optical disc master and mastering method using the multi-layer structure, and an optical disc manufactured using the optical disc master. More particularly, the invention relates to a multi-layer structure whose volume changes when its temperature exceeds a predetermined threshold, a method of drawing the microscopic structure that involves emitting a laser beam onto the multi-layer structure to create a temperature distribution within a beam spot and performing microscopic recording on a portion of the beam spot having a temperature higher than the threshold, an optical disc master and mastering method using the multi-layer structure, and an optical disc manufactured using the optical disc master.
2. Description of the Related Art
Currently, a resist pattern on a master used to manufacture an optical disc is fabricated by emitting a laser beam onto a photosensitive resist layer to produce an image and then developing the resist layer. The minimum size of the resist pattern is restricted due to the diffraction of the beam.
Thus, as part of the efforts to further reduce the minimum size of the resist pattern, research into new exposure technologies using deep-violet light, laser light, and soft X-rays has been conducted over several years. In particular, a KrF or ArF excimer laser is used to obtain a microscopic resist pattern with a size of about 150 nm. However, for realization of high-density optical discs, it is also necessary to solve problems in associated technologies such as the development of high-performance light sources and improvement of material characteristics for optical elements or resist pattern production.
Moreover, although reducing the diffraction of a beam may solve the above problems, it would likely result in a bulky light source or optical system as well as high energy consumption.
Another way to address the problems is electron beam lithography that uses an electron beam to fabricate nano structures with dimensions of a few nanometers, which is much smaller than in typical optical lithography. However, since electrons must be accelerated or deflected in a vacuum, a separate vacuum vessel and a large electrode or power supply for electron acceleration and deflection are required. Furthermore, a high acceleration voltage (for example, several tens of kilovolts) raises concerns about safety.
Still another approach is disclosed in Japanese Patent Laid-open Application No. 2002-365806, which describes a material and method of drawing a pattern on resist by heat generated by a laser. The proposed method includes heating up a resist layer overlying a layer consisting of an alloy of germanium, antimony, and tellurium (Ge2Sb2Te5) to cause chemical reaction using the Ge2Sb2Te5 layer as a light absorption thermal transformation layer, and drawing a microscopic pattern. This method not only enables the fabrication of nanostructures with dimensions of 100 nm, but also significantly reduces manufacturing costs due to the use of an inexpensive semiconductor laser as a light source. However, since the resist layer is heated with the light absorption thermal transformation layer, this makes the size and shape of the microscopic pattern unstable.